US9270393B2 - Method and system for reducing amplitude modulation (AM) noise in AM broadcast signals - Google Patents

Method and system for reducing amplitude modulation (AM) noise in AM broadcast signals Download PDF

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US9270393B2
US9270393B2 US13/721,396 US201213721396A US9270393B2 US 9270393 B2 US9270393 B2 US 9270393B2 US 201213721396 A US201213721396 A US 201213721396A US 9270393 B2 US9270393 B2 US 9270393B2
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signal
noise
captured
unit
broadcast
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US20140177843A1 (en
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Yao H. Kuo
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Visteon Global Technologies Inc
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Priority to DE102013114198.6A priority patent/DE102013114198B4/de
Priority to JP2013262286A priority patent/JP5774671B2/ja
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04H—BROADCAST COMMUNICATION
    • H04H20/00—Arrangements for broadcast or for distribution combined with broadcast
    • H04H20/86—Arrangements characterised by the broadcast information itself
    • H04H20/88—Stereophonic broadcast systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/06—Receivers
    • H04B1/10—Means associated with receiver for limiting or suppressing noise or interference
    • H04B1/1027—Means associated with receiver for limiting or suppressing noise or interference assessing signal quality or detecting noise/interference for the received signal
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/02—Transmitters
    • H04B1/04—Circuits
    • H04B1/0475—Circuits with means for limiting noise, interference or distortion
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/02—Transmitters
    • H04B1/04—Circuits
    • H04B1/0483—Transmitters with multiple parallel paths

Definitions

  • AM broadcasting is a process of radio broadcasting that was the first method of impressing sound on a radio signal and is still widely used today.
  • AM broadcasting signal has low immunity from interfering signals.
  • FIG. 1 shows that during an AM signal travel from a broadcasting antenna tower 102 to an AM receiver antenna 104 coupled to an AM broadcast receiving device or apparatus 106 , many possible noise signals may become add-on or interference signals to the original AM signal.
  • These interference noise signals can be generated by a number of sources, such as power-line noise, lightning, other wireless communications, etc. . . . .
  • These interference noise signals are captured together with the AM broadcast signal by the receiver circuit to become an in-band noise.
  • AM broadcast receiving apparatus 106 when AM broadcast receiving apparatus 106 is installed in a car, electrical motor noise and electromagnetic interferences generated by the car's electrical circuits/devices may increase the noise interference to the original AM broadcast signal.
  • Disclosed herein are improved a method and system for reducing AM noise in AM broadcast signals.
  • a computer-implemented method for reducing a noise signal added to an amplitude modulated (AM) broadcast signal while travelling from a broadcasting antenna to a receiving antenna includes capturing a signal representative of the AM broadcast signal corrupted by the noise signal via the receiving antenna, inverting the captured signal, and determining a carrying frequency of the AM broadcast signal and delaying the inverted waveform by a fraction of a cycle of the carrying frequency.
  • AM amplitude modulated
  • the method further includes generating a difference signal by subtractively combining the captured signal and the delayed inverted signal, generating an estimate noise signal by reducing an amplitude of the generated difference signal using a noise-reduction control multiplier, and minimizing the corrupting noise signal component of the captured signal by subtractively combining the captured signal and the generated estimate noise signal.
  • the computer-implemented method further includes filtering captured signal prior to the signal inversion.
  • the computer-implemented method further includes processing the captured signal through a low noise amplifying unit.
  • the computer-implemented method further includes processing the captured signal through an analog to digital converting unit to generate a digital version of the captured signal prior to the signal inversion.
  • the noise-reduction control multiplier is equal to a rational number 1/n with n being a number that is greater than a first value equal to about one (1) and is less than a second value equal to about two (2).
  • a computer readable storage medium having stored therein instructions executable by a computing element to cause the computing element to perform the above-introduced method.
  • FIG. 1 is a schematic diagram illustrating an embodiment of an AM broadcast signal corrupted by a number of interfering signals and captured by a receiver antenna;
  • FIGS. 2A-B are two graphs illustrating an uncorrupted AM broadcast signal and one of its period that has been inverted and delayed by a half-cycle;
  • FIG. 3 is a graph illustrating an AM broadcast signal with a predetermined amplitude modulation on a signal carrier
  • FIG. 4 is a graph illustrating a zoomed section of the AM broadcast signal of FIG. 3 ;
  • FIG. 5 is a graph illustrating a near-symmetrical characteristics of an upper half-cycle and of an inverted lower half-cycle of a waveform cycle of the zoomed signal section of FIG. 4 ;
  • FIG. 6 is a block diagram illustrating an exemplary embodiment of a system, that includes an analog signal processing unit, for reducing AM noise captured by an AM receiver;
  • FIG. 7 is a flow chart illustrating an example embodiment of a method for reducing AM noise using the analog signal processing unit of FIG. 6 ;
  • FIG. 8 is a block diagram illustrating an exemplary embodiment of a system, that includes a digital signal processing unit, for reducing an in-band AM noise signal captured by an AM receiver;
  • FIG. 9 is a flow chart illustrating an example embodiment of a method for reducing AM noise using the digital signal processing unit of FIG. 8 ;
  • FIG. 10 is a block diagram illustrating another exemplary embodiment of a system, that includes another digital signal processing unit, for reducing an in-band AM noise signal captured by an AM receiver;
  • FIG. 11A-C are three graphs that illustrate a corrupted AM broadcast signal, and a demodulated noise signal that corrupted the AM broadcast signal;
  • FIGS. 12A-C are three graphs that illustrate the corrupted AM broadcast signal of FIG. 4A after a reduction of the demodulated noise signal of FIG. 4C , which has been achieved with a value of an adaptive control factor selected by one of the corresponding systems shown in FIGS. 2 and 3 ;
  • FIGS. 13A-C are three graphs that illustrate the corrupted AM broadcast signal of FIG. 4A after another reduction of the demodulated noise signal of FIG. 4C , which has been achieved with another value of the adaptive control factor selected by one of the corresponding systems shown in FIGS. 2 and 3 ;
  • FIG. 14 is a graph illustrating an embodiment of another uncorrupted AM broadcast signal
  • FIG. 15 is a graph illustrating the AM broadcast signal of FIG. 14 as corrupted by a couple of interfering signals
  • FIG. 16 is a graph illustrating a composite of the signals interfering the AM broadcast signal of FIG. 15 ;
  • FIG. 17 is a graph illustrating an embodiment of an AM broadcast signal output by one of systems of FIGS. 6 , 8 , and 10 after reduction of the interfering signals of FIG. 16 ;
  • FIG. 18 is a graph illustrating an embodiment of an AM broadcast signal output by one of systems of FIGS. 6 , 8 , and 10 after reduction of the interfering signals of FIG. 16 ;
  • FIG. 19 is a schematic drawing illustrating a computing network system according to an exemplary embodiment.
  • noise suppression systems are known to use a noise generator coupled to a noise canceller.
  • One such noise suppression system may include a tuner configured to selectively receive a radio wave signal and to transform it into an electric signal, a field information detector to detect electric field information of the radio wave signal received by the tuner, a noise data generator that generate a noise pattern on the basis of the detected electric field information, a noise canceler configured to remove a noise component from the signal outputted from the tuner on the basis of the noise pattern generated by the noise data generator.
  • these noise data generators are known to lack the accuracy to generate a noise signal that can be considered a substantial reproduction of the captured noise signal.
  • an embodiment of the proposed noise reducing method is configured to process and analyze “near-symmetric” characteristics of a received AM broadcast signal.
  • the proposed method is configured to produce noise signals that are substantially similar to the original add-on noise signals.
  • the reproduced noise signals are then used to cancel substantially all or at least the majority of the add-on noise signals before the AM de-modulation process of the received AM broadcast signal.
  • a carrier wave or carrier is a waveform (usually sinusoidal) that is modulated (modified) with an input signal for the purpose of conveying information.
  • This carrier wave is usually a much higher frequency than the input signal.
  • the purpose of the carrier is usually either to transmit the information through space as an electromagnetic wave (as in radio communication), or to allow several carriers at different frequencies to share a common physical transmission medium by frequency division multiplexing (as, for example, a cable television system).
  • waveform 202 represents un-modulated AM carrier waveform at 300 KHz without interference.
  • waveform 202 is a smooth repetitive oscillating waveform with a periodically constant amplitude, i.e., peak deviation from zero.
  • waveform 202 includes a positive peak A 204 and a negative peak B 206 .
  • AM broadcast signal waveform 302 with a predetermined amplitude modulation on a signal carrier waveform (not shown) is illustrated.
  • AM broadcast waveform 302 has a frequency of 1.5 KHz and a 95% amplitude-modulation on the waveform carrier with a 300 KHz frequency.
  • Zoomed-in section 304 corresponds to a waveform section associated with time points T1 and T2, which are close to about 3 ⁇ 10 ⁇ 4 seconds and about 4 ⁇ 10 ⁇ 4 seconds, respectively.
  • waveform 502 representing a zoomed-in section 404 of waveform 402 of FIG. 4 is shown.
  • the zoomed section corresponds to a waveform section associated with time points T3 and T4, which are equal to about 374 ⁇ 10 ⁇ 6 seconds and about 390 ⁇ 10 ⁇ 4 seconds, respectively.
  • waveform 502 includes an upper cycle peak “C” that has a magnitude equal to +4.578062, and an adjacent lower cycle peak “D” that has a magnitude equal to ⁇ 4.81467.
  • upper cycle peak “C” is close to but not exactly the same as “inverted lower cycle peak “D.”
  • waveform 502 is a “Near Symmetrical” waveform.
  • a lower modulation index (%) leads to a more symmetrical waveform. Further, a higher audio and carrier frequency ratio leads to a more symmetrical waveform. Also, a lower modulation frequency leads to a more symmetrical waveform.
  • a schematic diagram 600 illustrates an exemplary embodiment of an analog system 602 for reducing noise signals added to an AM broadcast signal.
  • system 602 includes an antenna 604 for capturing an AM broadcast signal 606 augmented with add-on noise signals 608 and 610 .
  • Captured AM broadcast signal 606 is a signal based on airwaves transmitted from a broadcasting station (not shown).
  • System 602 further includes a cable unit 612 for communicating AM broadcast signal 606 to a filter and low-noise amplifier combination unit 614 , hereafter referred to as F&LNA unit 614 , and an analog signal processing unit 616 for AM noise reduction.
  • the filter of F&LNA unit 614 can be a two pole bandpass filter.
  • analog signal processing unit 616 hereafter referred to as analog AM noise reducing unit, includes a signal inverting unit 618 , a signal delaying unit 620 , a signal subtracting and reducing unit 622 , and a signal subtracting unit 624 .
  • a flow chart 700 illustrates an example embodiment of a method for reducing/minimizing add-on noises using analog AM noise reducing unit 616 .
  • F&LNA unit 614 processes AM broadcast signal 606 to output AM signal 607 .
  • AM noise reducing unit 616 is configured to provide AM signal 607 to signal inverting unit 618 .
  • signal inverting unit 618 processes it to output inverse AM signal 609 , at step 704 .
  • AM noise reducing unit 616 provides AM signal 609 to signal delaying unit 620 that is configured to delay AM signal 609 by about a half carrier cycle and to output resulting AM signal 611 .
  • AM noise reducing unit 616 provides both AM signal 607 and AM signal 611 to signal subtracting and reducing unit 622 , which proceeds to subtractively combine them, at step 708 , and to change an amplitude of the resulting difference signal by multiplying it with a rational number that is less than or equal to one (1), at step 710 .
  • This rational number can be selected to be equal to about 1/n where n satisfies the following inequality: 1 ⁇ n ⁇ 2.
  • the reduced difference signal 613 represents a generated or re-produced noise signal that is substantially similar to combined add-on noise signals 608 and 610 .
  • AM noise reducing unit 616 provides both AM signal 607 and reduced difference signal 613 to signal subtracting unit 624 , which is configured to subtractively combine them and output an AM noise-reduced signal 615 , which is desirably substantially similar to AM broadcast signal 606 .
  • AM noise reducing unit 616 substantially reduces add-on noise signals 608 and 610 when n is close to 2.
  • an optimal control value of n can be determined adaptively by this noise reduction approach during an on-going processing of AM broadcast signal 606 .
  • This optimal control value of n represents a value that best minimizes add-on noise signals 608 and 610 .
  • a schematic diagram 800 illustrates an exemplary embodiment of a digital system 802 for reducing noise signals added to an AM broadcast signal.
  • system 802 includes an antenna 804 for capturing an AM broadcast signal 806 augmented with add-on noise signals 808 and 810 .
  • System 802 further includes a cable unit 812 for communicating captured AM broadcast signal 806 to a filter and low-noise amplifier combination unit 814 , hereafter referred to as F&LNA unit 814 , an analog to digital (A/D) signal converting unit 819 , and a digital signal processing unit 816 for AM noise reduction.
  • the filter of F&LNA unit 814 can be a two pole bandpass filter. As shown in FIG.
  • analog signal processing unit 816 hereafter referred to as digital AM noise reducing unit, includes a signal inverting unit 818 , a signal delaying unit 820 , a signal subtracting and reducing unit 822 , a delay compensation unit 823 , a signal subtracting unit 824 , an AM demodulating unit 826 , an error control calibration unit 828 , and a digital to analog (D/A) converting unit 830 .
  • digital AM noise reducing unit includes a signal inverting unit 818 , a signal delaying unit 820 , a signal subtracting and reducing unit 822 , a delay compensation unit 823 , a signal subtracting unit 824 , an AM demodulating unit 826 , an error control calibration unit 828 , and a digital to analog (D/A) converting unit 830 .
  • D/A digital to analog
  • a flow chart 900 illustrates an example embodiment of a method for reducing/minimizing add-on noises using digital AM noise reducing unit 816 .
  • F&LNA unit 814 processes AM broadcast signal 806 to output AM signal 807 .
  • A/D signal converting unit 819 is configured to convert AM signal 807 to a digital signal 809 .
  • AM noise reducing unit 816 is configured to provide AM digital signal 809 to signal inverting unit 818 , at step 904 .
  • signal inverting unit 818 processes it to output inverse AM digital signal 811 , at step 906 .
  • AM noise reducing unit 816 provides AM digital signal 811 to signal delaying unit 820 that is configured to delay AM digital signal 811 by about a half carrier cycle and to output resulting AM signal 813 , at step 908 .
  • AM noise reducing unit 816 provides both AM signal 807 and AM signal 813 to signal subtracting and reducing unit 822 , which proceeds to subtractively combine them, at step 910 , and to change an amplitude of the resulting difference signal by multiplying it with a rational number that is less than or equal to one (1), at step 912 .
  • the rational number can be selected to be equal to 1/n where n satisfies the following inequality: 1 ⁇ n ⁇ 2.
  • the reduced difference signal 815 represents a re-produced noise signal that is desirably substantially similar to combined add-on noise signals 808 and 810 .
  • AM noise reducing unit 816 provides AM signal 809 to delay compensation unit 823 , which is configured to apply a compensating time delay to AM signal 809 , and output AM delay-compensated signal 817 .
  • AM noise reducing unit 816 is configured to provide both AM delay-compensated signal 817 and reduced difference signal 815 to signal subtracting unit 824 , which is configured to subtractively combine them and output an AM noise-reduced signal 819 , which is substantially similar to AM broadcast signal 806 .
  • AM noise-reduced signal 819 is demodulated by AM demodulating unit 826 , and the resulting demodulated signal 821 is provided to D/A converting unit 830 that converts it into an analog waveform prior to being outputted as an audio signal by a receiving speaker (not shown).
  • error control and calibration unit 828 is recruited to analyze demodulated signal 819 and use results of the analysis to adjust as needed the rational number 1/n that is used by signal subtracting and reducing unit 822 in order to improve on the minimization of add-on noise signals 808 and 810 .
  • a schematic diagram 800 illustrates another exemplary embodiment of a digital system 1002 for reducing noise signals added to an AM broadcast signal.
  • Digital system 1002 has substantially similar components as those of digital system 802 , except that F&LNA unit 1014 further includes a radio processing unit and error control and calibration unit 1028 is further coupled to signal delaying unit 1020 .
  • F&LNA unit 1014 is configured to identity an intermediate frequency (IF) of AM broadcast signal 1006 , to extract from it a signal, denoted IF signal 1007 having the identified intermediate frequency as its main frequency.
  • IF intermediate frequency
  • the coupling of error control and calibration unit 1028 to signal delaying unit 1020 serves to control the signal delaying process to further improve on the noise reduction process.
  • signal delaying unit 1020 adaptively adjusts an amount of signal delay that can be different from a half carrier cycle delay and still leads to a better minimization of add-on noise signals 808 and 810 .
  • FIGS. 11A-C three graphs are shown that illustrate a corrupted AM broadcast signal 1102 , a zoomed section 1104 of AM broadcast signal 1102 , and an add-on noise signal 1106 that corrupted AM broadcast signal 1102 .
  • FIG. 11A illustrates AM broadcast signal 1102 that was selected to represent AM broadcast signal waveform 302 of FIG. 3 corrupted with add-on noise signals.
  • a zoomed section of AM broadcast signal 1102 is illustrated in FIG. 11B .
  • the add-noise signal 1106 corresponding to the zoomed 1104 section is substantially determined.
  • FIG. 12A illustrates a resulting AM broadcast signal 1202 that represents AM broadcast signal 1102 with the reduced add-on noise signal 1106 .
  • FIG. 12B illustrates the zoomed section of AM broadcast signal 1102 shown in FIG. 11B after the noise reduction, and
  • FIG. 12C illustrates the reduced version of add-on noise signal 1106 .
  • noise reducing systems 602 , 802 , and 1002 are configured to adaptively vary the value of adjusting control factor n.
  • adjusting control factor n was selected to be equal to 1.5, which lead to a further reduction of add-on noise signal 1106 as illustrated in a further smoother waveform of AM broadcast signal 1102 , and a further reduced amplitude-wise of add-on noise signal 1106 , shown in FIGS. 13A and 13C .
  • a graph 1400 illustrates an embodiment of an uncorrupted AM broadcast signal 1402 provided with a substantially perfect signal modulation.
  • AM broadcast signal 1402 has a frequency of 1.7 KHz and is amplitude-modulated by a 300 KHz waveform carrier (not shown).
  • AM broadcast signal 1402 is corrupted by a couple of add-on noise signals.
  • These interfering noise signals are both frequency modulated (FM) signals having frequencies equal to 3.33 KHz and 2.0 KHz, respectively, whose composite signal is illustrated by waveform 1602 of FIG. 16 .
  • the corrupted version of AM broadcast signal 1402 is illustrated by waveform 1502 of FIG. 15 .
  • a noise-reduced signal version of AM broadcast signal 1402 is generated as illustrated by waveform 1702 , shown in FIG. 17 .
  • the removed distorting component of waveform 1502 is illustrated by waveform 1802 of FIG. 18 .
  • each of noise reducing systems 602 , 802 , and 1002 include a processing unit and a memory unit.
  • Each of the processing units can be implemented on a single-chip.
  • various architectures can be used including dedicated or embedded microprocessor ( ⁇ P), a microcontroller ( ⁇ C), or any combination thereof.
  • Each of the memory units may be of any type of memory now known or later developed including but not limited to volatile memory (such as RAM), non-volatile memory (such as ROM, flash memory, etc.) or any combination thereof, which may store software that can be accessed and executed by the processing units, for example.
  • Each of the memory units are configured to store instructions that correspond to the processing functions of the above discussed noise reducing systems.
  • FIG. 19 is a schematic illustrating a conceptual partial view of an example computer program product 1900 that includes a computer program for executing a computer process on a computing device, arranged according to at least some embodiments presented herein.
  • the example computer program product 1900 is provided using a signal bearing medium 1901 .
  • the signal bearing medium 1301 may include one or more programming instructions 1902 that, when executed by one or more processors may provide functionality or portions of the functionality described above with respect to FIGS. 7 and 9 .
  • FIGS. 7 and 9 may be implemented as computer program instructions encoded on a non-transitory computer-readable storage media in a machine-readable format.
  • one or more features of blocks 702 , 704 , 706 , 708 and/or 710 and 902 , 904 , 906 , 908 , 910 and/or 912 , respectively, may be undertaken by one or more instructions associated with the signal bearing medium 1901 .
  • the signal bearing medium 1901 may encompass a non-transitory computer-readable medium 1903 , such as, but not limited to, a hard disk drive, a Compact Disc (CD), a Digital Video Disk (DVD), a digital tape, memory, etc.
  • the signal bearing medium 1901 may encompass a computer recordable medium 1904 , such as, but not limited to, memory, read/write (R/W) CDs, R/W DVDs, etc.
  • the signal bearing medium 1901 may encompass a communications medium 1905 , such as, but not limited to, a digital and/or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link, etc.).

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US13/721,396 2012-12-20 2012-12-20 Method and system for reducing amplitude modulation (AM) noise in AM broadcast signals Expired - Fee Related US9270393B2 (en)

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US13/721,396 US9270393B2 (en) 2012-12-20 2012-12-20 Method and system for reducing amplitude modulation (AM) noise in AM broadcast signals
DE102013114198.6A DE102013114198B4 (de) 2012-12-20 2013-12-17 Verfahren und System zum Mindern des amplitudenmodulierten (AM) Rauschsignals in AM-Rundfunksignalen
JP2013262286A JP5774671B2 (ja) 2012-12-20 2013-12-19 Ａｍ放送信号における振幅変調（ａｍ）ノイズを低減するための方法及びシステム

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JP6456703B2 (ja) * 2015-01-29 2019-01-23 本田技研工業株式会社 車両用ノイズキャンセリング装置
GB2560983B (en) * 2017-03-31 2019-08-07 Canon Kk Detector for detecting a wide band signal
DE102017207943A1 (de) * 2017-05-11 2018-11-15 Robert Bosch Gmbh Signalbearbeitungsvorrichtung für ein insbesondere in ein Batteriesystem einsetzbares Kommunikationssystem

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US20140177843A1 (en) 2014-06-26
JP2014123948A (ja) 2014-07-03

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